When I first took acid, I was going to take one tab, the white-on-white stuff that's always around here, anyway, I was going to take one, and then everybody I talked to said "take two, I took one and really wished I had taken two my first time".
So I took two and it was perfect. If those tabs are 90-120ug, you should take two. Not three, unless you're experienced with LSD to the point where you're comfortable with what it does and what it does when you take a lot. I personally feel that 150-200ug is the place to be.